Servo write head assembly and servo writer

ABSTRACT

A servo write head assembly comprises an AC demagnetizing head that slides in contact with a magnetic tape all of which surface is magnetized in one direction of longitudinal directions thereof, and demagnetizes a data band of the magnetic tape; a servo write head that slides in contact with the magnetic tape, magnetizes a servo band of the magnetic tape in a reverse direction, and writes a servo signal; and a guide for regulating a movement in lateral directions of the magnetic tape that is running, wherein the AC demagnetizing head and the servo write head are integrally configured and the guide is provided between the AC demagnetizing head and the servo write head.

This is a divisional of application Ser. No. 10/814,638 filed Apr. 1,2004. The entire disclosure(s) of the prior application(s), applicationSer. No. 10/814,638 is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a servo write head assembly and servowriter that write a servo signal in a magnetic tape for performingtracking-control of a magnetic head.

2. Description of the Related Art

These years, in a magnetic tape a high density recording has progressedand there is the tape having a capacity of around 100 gigabytes for abackup of a computer. Therefore, several hundreds of data tracks areformed in the magnetic tape in a lateral direction. Accordingly, a widthof a data track has extremely become narrow, and also a distance betweenadjacent data tracks has extremely become narrow. Therefore, in order tomake a recording/reproducing element of a magnetic head trace the datatrack, a servo signal is written in the magnetic tape in advance, andwith reading the servo signal by the magnetic head, a position thereof(position of the lateral direction of the magnetic tape) isservo-controlled (see Japanese Paten Laid-Open Publication No.Hei-8-30942).

And the servo signal is recorded on non magnetized magnetic tape so asto magnetize a servo band in one direction.

In other words, as shown in FIGS. 10A and 10B, conventional servosignals SS are formed on non magnetized servo bands SB by flowing arecording current pulse PC consisting of a zero current and a plus pulsecurrent as a recording current in order to avoid a saturation phenomenonof a servo read element (MR (Magneto Resistive) element). If such therecording current pulse PC is used, a magnetic tape MT is not magnetizedin areas except for servo patterns SP when the recording current pulsePC is the zero current; and when the plus pulse current of the recordingcurrent pulse PC flows, the servo patterns SP are magnetized in onedirection by leak magnetic fluxes from servo gaps, thereby as a resultthe servo signals SS being written.

On the other hand, in a magnetic tape recoding/reproducing apparatus achange point of a magnetization in the servo signals SS is detected witha change of an electric resistance by an MR element, and the changepoint of the magnetization as a read signal is output in a differentialwaveform (voltage value). Therefore, the larger the electric resistanceof the MR element becomes, the higher a peak voltage value of the readsignal of the servo signals SS, thereby an SN (Signal/Noise) ratio ofthe read signal being improved. Accordingly, when changes of the servosignals SS themselves are large and a read area is large due to a widewidth of the MR element, as shown in FIG. 10C a peak voltage value of aread signal RSL of the servo signals SS becomes high.

Whereas, hereafter the high density recording of the magnetic tape isforeseen to progress till around several tens of terabytes. Therefore, anumber of data tracks of the magnetic tape, the width of the data track,and the distance between the adjacent data tracks will become narrower,and the magnetic tape itself will become a thin layer. Based upon this,an amount of magnetism that is detectable in reading a servo signaldecreases and a change of a magnetization amount that is detectable withthe servo read element also becomes small. Accordingly, as shown in FIG.10D a peak voltage value of a read signal RSS of the servo signals SSbecomes small, thereby the SN ratio of the read signal RSS worsening. Asa result, in the magnetic tape recording/reproducing apparatus the servosignals SS becomes not able to be accurately read, thereby highlyaccurate position control of the magnetic head resulting in being notable to be performed.

Consequently, a servo write head assembly and servo writer, which canwrite a servo signal that is high in the SN ratio thereof, are stronglyrequested.

SUMMARY OF THE INVENTION

In order to solve the problems described above, a first aspect of thepresent invention is a servo write head assembly that comprises an ACdemagnetizing head that contacts a magnetic tape all of which surface ismagnetized in one direction of longitudinal directions thereof, anddemagnetizes a data band of the magnetic tape; a servo write head thatslides in contact with the magnetic tape, magnetizes a servo band of themagnetic tape in a reverse direction, and writes a servo signal; and aguide for regulating a movement in lateral directions of the magnetictape that is running, wherein the AC demagnetizing head and the servowrite head are integrally configured and the guide is provided betweenthe AC demagnetizing head and the servo write head.

The servo write head assembly writes the servo signal by the servo writehead magnetizing the servo band of the magnetic tape, all of whichsurface is magnetized in one direction of the longitudinal directionsthereof, for example, in a magnetic tape travel direction (thisdirection is referred to as “forward direction”), in the reversedirection. As a result, when the servo signal is read with a servo readelement, a change rate and change amount of a magnetic field at a changeportion of a servo pattern magnetized in the reverse direction for abase portion of the servo band magnetized in the forward directionbecome large, thereby an output of the servo signal becoming high.Accordingly, the servo write head assembly enables the servo signal,which is high in an SN ratio of a read signal thereof, to be written inthe magnetic tape.

In the write head assembly, for example, the AC demagnetizing headdemagnetizes nothing except for a data band out of the magnetic tape allof which surface is magnetized in the forward direction of thelongitudinal directions thereof. Accordingly, in recording a data signalon the data band the write head assembly enables the magnetic tape,where the data signal can be preferably recorded, to be obtained sincethe data signal to be recorded is not influenced by a magnetization(forward direction magnetization) originally recorded.

In addition, in the servo write head assembly a relative positionalrelationship of the AC demagnetizing head and the servo write head isfixed in accordance with the AC demagnetizing head and the servo writehead respectively integrated. And an oscillation in lateral directionsof the magnetic tape running between the AC demagnetizing head and theservo write head is regulated with the guide provided between the ACdemagnetizing head and the servo write head. Accordingly, the servowrite head assembly enables the magnetization of the servo band to beaccurately demagnetized and enables the servo signal to be accuratelywritten on the servo band.

Meanwhile, a position of the AC demagnetizing head may be at any ofupstream and downstream sides of the servo write head for the magnetictape travel direction.

A second aspect of the present invention is a servo write head assemblythat comprises a DC demagnetizing head that slides in contact with amagnetic tape that is running, and magnetizes at least a servo band ofthe magnetic tape in one direction of longitudinal directions thereof; aservo write head that is provided at a downstream side of a magnetictape travel direction of the magnetic tape of the DC demagnetizing head,slides in contact with the magnetic tape that is running, magnetizes theservo band in a reverse direction, and writes a servo signal; and aguide for regulating a movement in lateral directions of the magnetictape that is running, wherein the DC demagnetizing head and the servowrite head are integrally configured and the guide is provided betweenthe DC demagnetizing head and the servo write head.

In the write head assembly the DC demagnetizing head magnetizes any onedirection of longitudinal directions of the magnetic tape, for example,toward the forward direction. Next, the servo signal is written by theservo write head magnetizing the servo band magnetized in the forwarddirection in the reverse direction. As a result, since when reading theservo signal with a servo read element of a magnetic head, a change rateand change amount of a magnetic field at a change portion of a servopattern magnetized in the reverse direction for a base portion of theservo band magnetized in the forward direction become large, thereby anoutput of the servo signal becoming high. Accordingly, the servo writehead assembly enables the servo signal, which is high in the SN ratiothereof, to be written in the magnetic tape.

In addition, in the servo write head assembly a relative positionalrelationship of the DC demagnetizing head and the servo write head isfixed in accordance with the DC head and the servo write headrespectively integrated. And an oscillation in lateral directions of themagnetic tape running between the DC demagnetizing head and the servowrite head is regulated with the guide provided between the DCdemagnetizing head and the servo write head. Accordingly, the servowrite head assembly enables the magnetization of the servo band to beaccurately magnetized in one direction of the longitudinal directionsand enables the servo signal to be accurately written on the servo band.

A third aspect of the present invention is a servo writer that comprisesa magnetic tape running system that sends a magnetic tape, all of whichsurface is magnetized in one direction of longitudinal directions, outof a supply reel, and winds the magnetic tape with a winder, therebyrunning the tape; an AC demagnetizing head that slides in contact withthe magnetic tape that is running, and demagnetizes a servo band; aservo write head that slides in contact with the magnetic tape that isrunning, magnetizes a servo band of the magnetic tape in a reversedirection, and writes a servo signal,; and a guide for regulating amovement in lateral directions of the magnetic tape, wherein the ACdemagnetizing head and the servo write head are integrally configuredand the guide is provided between the AC demagnetizing head and theservo write head.

In the servo writer, for example, when the magnetic tape all of whichsurface is magnetized in the forward direction by a magnetic taperunning system, same as described in the first aspect of the presentinvention, the servo write head writes the servo signal by magnetizingthe servo band magnetized in the forward direction in the reversedirection. Accordingly, same as described in the first aspect of thepresent invention, the servo writer enables the servo signal, which ishigh in the SN ratio of a read signal thereof, to be written in themagnetic tape.

In addition, same as described in the first aspect of the presentinvention, the servo writer enables nothing except for the data band outof the magnetic tape, all of which surface is magnetized in the forwarddirection of longitudinal directions, to be demagnetized by the ACdemagnetizing head. Accordingly, the servo writer enables the magnetictape, where a data signal can be preferably recorded, to be obtainedsince the data signal is not influenced by a magnetization(magnetization in the forward direction) originally recorded.

In addition, the AC demagnetizing head and the servo write head areintegrally configured, and since the guide is provided between the ACdemagnetizing head and the servo write head, same as described in thefirst aspect of the present invention, the relative positionalrelationship of the AC demagnetizing head and the servo write head isfixed and an oscillation in lateral directions of the magnetic taperunning between the AC demagnetizing head and the servo write head isregulated. Accordingly, same as described in the first aspect of thepresent invention, the servo writer enables the magnetization of theservo band to be accurately magnetized in one direction of longitudinaldirections and enables the servo signal to be accurately written on theservo band.

A fourth aspect of the present invention is a servo writer thatcomprises a magnetic tape running system that sends a magnetic tape outof a supply reel, and winds the magnetic tape with a winder, therebyrunning the tape; a DC demagnetizing head that slides in contact withthe magnetic tape that is running, and magnetizes at least a servo bandof the magnetic tape in one direction of longitudinal directions; aservo write head that is provided at a downstream side of a magnetictape travel direction of the DC demagnetizing head, slides in contactwith the magnetic tape that is running, magnetizes the servo band in areverse direction, and writes a servo signal; and a guide for regulatinga movement in lateral directions of the magnetic tape that is running,wherein the DC demagnetizing head and the servo write head areintegrally configured and the guide is provided between the DCdemagnetizing head and the servo write head.

In the servo writer, for example, when the magnetic tape runs, same asdescribed in the second aspect of the present invention, the DCdemagnetizing head magnetizes the servo band toward the forwarddirection of the magnetic tape and the servo write head writes the servosignal by magnetizing the servo band magnetized in the forward directionin the reverse direction. Accordingly, same as described in the secondaspect of the present invention, the servo writer enables the servosignal, which is high in the SN ratio of a read signal thereof, to bewritten in the magnetic tape.

In addition, in the servo writer the DC demagnetizing head and the servowrite head are integrally configured, and since the guide is providedbetween the DC demagnetizing head and the servo write head, same asdescribed in the second aspect of the present invention, the relativepositional relationship of the DC demagnetizing head and the servo writehead is fixed and an oscillation in lateral directions of the magnetictape running between the DC demagnetizing head and the servo write headis regulated. Accordingly, same as described in the second aspect of thepresent invention, the servo writer enables the portion of the servoband to be accurately magnetized in one direction of longitudinaldirections and enables the servo signal to be accurately written on theservo band.

Meanwhile, in the first to fourth aspects of the present invention “tobe integrally configured” includes being configured by joining twocomponents into one.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration drawing of a servo writer of a firstembodiment.

FIG. 2 is a perspective view showing an appearance around a first guideof the servo writer of FIG. 1.

FIG. 3 is a drawing showing an appearance where the first guide of FIG.2 is seen from an arrow direction X of FIG. 2.

FIG. 4 is a plan view of a servo write head used for the servo writer ofFIG. 1.

FIG. 5. is a drawing illustrating a manufacturing process of a pancakethat is set on a supply reel so the servo writer of FIG. 1.

In FIGS. 6A, 6B, and 6C, FIG. 6A is an enlarged plan view illustrating amagnetization state of a magnetic tape magnetized by the servo writer ofFIG. 1; FIG. 6B is a drawing showing a servo signal read from themagnetic tape of FIG. 6A; and FIG. 6C is a drawing showing a signal inwriting the servo signal.

FIG. 7 is a configuration drawing of a servo writer of a secondembodiment.

FIG. 8 is an enlarged plan view illustrating a magnetization state of amagnetic tape magnetized by the servo writer of FIG. 7.

In FIGS. 9A and 9B, FIG. 9A is a perspective view of a servo write headassembly used for a servo writer of another embodiment; and FIG. 9B is asection view taken along a line Y—Y of FIG. 9A.

FIGS. 10A to 10D are drawings illustrating a magnetic tape having aconventional servo signal: FIG. 10A is a drawing showing a recordingcurrent in writing the servo signal; FIG. 10B is a plan view of themagnetic tape; FIG. 10C is a drawing showing a read signal when a widthof a read element is wide; and FIG. 10D is a drawing showing anotherread signal when the width of the read element is narrow.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[First Embodiment]

Hereinafter, the embodiments of the present invention will be described,referring to FIGS. 1 to 4 as needed.

As shown in FIG. 1, a servo writer 20 A mainly comprises a supply reel21 a, a winder 22, a drive unit 23, a pulse generation circuit 24 a, aservo write head 25, an AC demagnetizing head 27, a control unit 26 a,first guides 29 a, and second guides 29 b. In addition, in the servowriter 20A is also provided a power source unit, a cleaning unit forcleaning a magnetic tape MT, a verification unit for inspecting writtenservo signals, and the like, which are not shown.

On the supply reel 21 a the magnetic tape MT, which is slit into aproduct width from a wide whole web before servo signals are writtentherein, is set as a large diameter winding of a pancake, and the supplyreel 21 a is configured so as to send out the magnetic tape MT inwriting the servo signals. Meanwhile, in the magnetic tape MT anorientation treatment is performed in a process for manufacturing apancake shaped magnetic tape described later, and in advance, allsurface of the magnetic tape MT is magnetized in one direction oflongitudinal directions thereof, to be more precise, in a magnetic tapetravel direction, that is, in the forward direction.

The winder 22 is configured so as to wind the magnetic tape MT that issent out of the supply reel 21 a and guided with the first guides 29 aand the second guides 29 b.

The drive unit 23 is a unit for rotationally driving the winder 22, andcomprises a motor, a motor drive circuit for supplying a motor current,a gear for coupling a motor shaft and the winder 22, and the like whichare not shown. The drive unit 23 generates the motor current in themotor drive circuit, based on a motor current signal from the controlunit 26 a, supplies the motor current to the motor, and furthermore,transmits rotation drive force of the motor to the winder 22 through thegear, thereby rotating the winder 22.

The pulse generation circuit 24 a is a circuit for generating arecording current pulse PC1 (see FIG. 6C) described later, and comprisesvarious electronic components. And the pulse generation circuit 24 a isconfigured so as to generate the recording current pulse PC1, based on apulse control current from the control unit 26 a. In addition, the pulsegeneration circuit 24 a is configured so as to continuously give analternating current demagnetizing current for the AC demagnetizing head27.

The control unit 26 a is a unit for controlling operation of each partof the servo writer 20A, and comprises a CPU (Central Processing Unit),various memory units, and the like. In order to make a magnetic taperunning speed constant in writing the servo signals, the control unit 26a generates the motor current signal for controlling the motor currentof the drive unit 23, and sends it to the drive unit 23. In addition,the control unit 26 a generates a pulse control signal for generatingthe recording current pulse PC1 (see FIG. 6C) at the pulse generationcircuit 24 a and is configured so as to send the pulse control signal tothe pulse generation circuit 24 a. In addition, the control unit 26 agenerates a demagnetization control signal for generating thealternating current demagnetizing current at the pulse generationcircuit 24 a and is configured so as to send the alternating currentdemagnetizing current to the pulse generation circuit 24 a.

The servo write head 25 and the AC demagnetizing head 27 are, as shownin FIG. 2, arranged so as to slide in contact with the magnetic tape MTthat is running by being guided with the second guides 29 b. And in theservo writer 20A the servo write head 25 is arranged at an upstream sidein the magnetic tape travel direction; the AC demagnetizing head 27 isarranged at a downstream in the magnetic tape travel direction.

The servo write head 25 and the AC demagnetizing head 27 are integrallyconfigured with being connected to a support member 30 a fixed at aplatform not shown, and both tops thereof, which respectively extendfrom the support member 30 a and respectively slide in contact with themagnetic tape MT, form a gap with a distance. In the gap a pair of thefirst guides 29 a described next are designed to be arranged.

Here, as obvious referring to FIG. 3 in combination, the pair of theguides 29 a are configured of rollers 32 a for holding down a surface ofthe magnetic tape MT with circumferential surfaces thereof and flanges32 b for holding down side edges of the magnetic tape MT that isrunning.

Each of the pair of the first guides 29 a is oppositely arranged eachother at the gap between the servo write head 25 and the ACdemagnetizing head 27 SO as to pinch the magnetic tape MT, which isrunning between them, from lateral directions thereof.

These first guides 29 a are attached to disc springs 31 and arranged atthe gap. Bases of the disc springs 31 are fixed at a shaft member 33 forrotatably supporting one of the second guides 29 b that extends from thebases not shown, and at tops extending from the shaft member 33, thedisc springs 31 rotatably support the first guides 29 a. And each of thefirst guides 29 a is designed to push each side edge of the magnetictape MT oscillated in lateral directions with a minute energizing forceF. The energizing force F is preferably 0.490×10⁻² to 7.84×10⁻² N andmore preferably 0.490×10⁻² to 3.92×10⁻² N.

The servo write head 25 is a magnetic head for writing a servo signal,comprises a coil (not shown) for generating a magnetic flux by therecording current pulse PC1 (see FIG. 6C) being given from the pulsegeneration circuit 24 a, and as shown in FIG. 4, head gaps 25 a areformed. In the servo write head 25 four pieces of the head gaps 25 a arearranged in a line, corresponding to lateral direction positions of fourpieces of the servo bands SB1 formed on the magnetic tape MT. The headgaps 25 a are formed by a lithography where semiconductor technology isapplied, and have a bottom-open unparallel reverse V letter shape with apredetermined angle for longitudinal directions of the magnetic tape MT.

The AC demagnetizing head 27 is a head for demagnetizing a portioncorresponding to data bands of the magnetic tape MT by magnetizing theportion with an alternating current. The AC demagnetizing head 27comprises a coil (not shown) for generating a magnetic flux by analternating current demagnetizing current given from the pulsegeneration circuit 24 a. And on a sliding contact surface of themagnetic tape MT of the AC demagnetizing head 27, magnetic gaps (notshown) for a demagnetization are provided at positions corresponding todata bands of the magnetic tape MT. Of course, the AC demagnetizing head27 may be configured so as not to demagnetize a portion of servo bands,and may also be configured so as to demagnetize a portion except for thedata bands and servo bands of the magnetic tape MT which portion is notused for recoding data, for example, guard bands GB1 (see FIG. 6A)formed at both edges of the magnetic tape MT in longitudinal directionsthereof.

Next, operation of the servo writer 20A of the embodiment will bedescribed, referring to FIGS. 5 and 6.

First, on the supply reel 21 a of the servo writer 20A (see FIG. 1) isset a pancake shape of the magnetic tape MT after a slit. The pancakeshape of the magnetic tape MT is manufactured as shown in FIG. 5 bypassing a base film BF through a coating process 11, an orientationprocess 12, a drying process 13, a calendar process 14, and a slittingprocess 15. Meanwhile, the magnetic tape MT that has finished till theslitting process 15 is a tape where a servo signal is not yet recorded.

All surface of the magnetic tape MT is magnetized in one direction(forward direction) by a web W, where a magnetic paint is coated in thecoating process 11, passing through a place where same polarities (Npolarities in FIG. 5) of two magnets 12 a and 12 b are made opposite.

After such the pancake shape of the magnetic tape MT is set at thesupply reel 21 a, a top of the magnetic tape MT is joined on a core ofthe winder 22.

Next, when the drive unit 23 rotates the winder 22 by the motor currentsignal from the control unit 26 a, the magnetic tape MT runs by beingwound with the winder 22 while the second guides 29 b and the like guidethe tape MT. And servo signals SS1 are written by the servo write head25 sliding in contact with the tape MT that is running.

Then, the pulse generation circuit 24 a generates, as shown in FIG. 6C,a plus pulse current PP1 of a plus polarity, a zero current ZC1, anotherplus pulse current PP1, and another zero current ZC1 in this order,based on the pulse control signal from the control unit 26 a, and thenrepeats a pattern where no current (zero current ZC) for a predeterminedtime is generated, thereby generating a recording current pulse PC1.Meanwhile, at that time the control unit 26 a generates, as shown inFIG. 6A, the pulse control signal for controlling a current, pulsewidth, and generation timing of the plus pulse currents PP1 of therecording current pulse PC1 and sends them to the pulse generationcircuit 24 a, in order to set a servo signal that prescribes apredetermined interval for forming the patterns SP1 and a width oflongitudinal directions thereof.

If a pulse train of the recording current pulse PC1 is thus flowed at apredetermined pattern from the control unit 26 a to the coil of theservo write head 25, a magnetic layer of the magnetic tape MT ismagnetized in a reverse direction by a leak magnetic flux from the headgaps 25 a when the plus pulse currents PP1 flow in the coil; and themagnetic layer of the magnetic tape MT is not magnetized when therecording current pulse PC1 is the zero currents ZC1. As a result, theservo patterns SP1 magnetized in the reverse direction are formed on abase portion of the servo bands SB1 magnetized in the forward directionof the magnetic tape MT. Of course, a portion of the servo bands SB1except for the servo patterns SP1 is magnetized in the forward directionas it is.

Meanwhile, a current of the plus pulse currents PP1 at this time issufficient one for magnetizing the magnetic layer of the magnetic tapeMT by the leak magnetic flux from the head gaps 25 a, and is set bytaking such characteristics of the coil of the servo write head 25 intoconsideration. In addition, a pulse width (time) of the plus pulsecurrents PP1 can prescribe a predetermined width of the servo patternsSP1 in the longitudinal directions, and is set by taking a running speedof the magnetic tape MT, a shape of the head gaps 25 a of the servowrite head 25, and the like into consideration (see FIG. 4). Inaddition, a predetermined time of the zero currents ZC1 can prescribethe predetermined interval for forming the servo patterns SP1, and isset by taking the running speed of the magnetic tape MT and the likeinto consideration.

And the AC demagnetizing head 27 provided at the downstream side of themagnetic tape travel direction of the servo write head 25 demagnetizes aportion corresponding to the data bands DB1 of the magnetic tape MT. Thewinder 22 winds the demagnetized magnetic tape MT.

In such the servo writer 20A of the embodiment the servo write head 25and the AC demagnetizing head 27 are integrally configured (see FIG. 2)and the first guides 29 a (see FIG. 3) regulate a movement in thelateral directions of the magnetic tape MT, which is running between theservo write head 25 and the AC demagnetizing head 27, by the energizingforce F of the disc springs 31. As a result, in the servo writer 20A asliding contact surface of the AC demagnetizing head 27 with themagnetic tape MT is generally long, so even if a distance between thesecond guides 29 b (see FIG. 1) arranged at the upstream/downstreamsides of the AC demagnetizing head 27 is obliged to be taken wide, themagnetic tape MT is not oscillated in the lateral directions thereofbetween the servo write head 25 and the AC demagnetizing head 27.Accordingly, the servo writer 20A can accurately demagnetize nothingexcept for the portion of the data bands DB1 and leave a magnetizationin the forward direction of the portion of the servo bands SB1. Inaddition, since in accordance with the servo writer 20A of theembodiment a curvature of servo bands SB1 extending in the longitudinaldirections of the magnetic tape MT can be restrained by preventingoscillations of the lateral directions of the magnetic tape MT, aposition error signal (PES) is reduced.

The magnetic tape MT where a magnetization treatment is performed bysuch the servo writer 20A has, as obvious again referring to FIG. 6A, aplurality of the servo bands SB1 extending in the longitudinaldirections of the magnetic tape MT and each of the data bands DB1positioned between each two of the servo bands SB1. Each of the servobands SB1 is magnetized in the magnetic tape travel direction (forwarddirection) of the longitudinal directions. The magnetization is shown bysmall arrow marks in FIG. 6A. And the servo signals SS1 are written withmagnetizing the servo bands SB1 in the reverse direction. The servosignals SS1 form each of servo patterns SP1 by: a burst Ba that is amagnetization portion like two stripes making a positively slanted anglefor the travel direction of the magnetic tape MT; and a burst Bb that isfollowing the burst Ba and is the magnetization portion like two stripesmaking a negatively slanted angle for the travel direction. And theservo patterns SP1 are repeatedly formed at a predetermined distance inthe longitudinal directions, thereby the servo signals SS1 beingconfigured. And each of the data bands DB1 between each two of the servobands SB1 is demagnetized by the AC demagnetizing head 27. Thus, themagnetic tape MT, where the servo signals SS1 are written and wound onthe winder 22, is slit into a tape length depending on a productspecification, and then is housed in a cartridge case and the like (notshown).

Meanwhile, although in the embodiment each of the servo patterns SP1 isconfigured of each two of positively slanted stripes and negativelyslanted stripes, it is variable as needed, for example, such as beingconfigured of each five of the positively slanted stripes and thenegatively slanted stripes; and being alternately configured of eachfive of the positively slanted stripes and the negatively slantedstripes and each four of the positively slanted stripes and thenegatively slanted stripes. In addition, in FIG. 6A the servo patternsSP1 are drawn comparatively large for the magnetic tape MT in order tobe easily understood.

In FIG. 6A is shown a positional relationship of a magnetic head H forthe magnetic tape MT. In the magnetic head H servo read elements SH forreading the servo signals SS1 are parallely provided in a lateraldirection of the magnetic tape MT at a same distance as that of aplurality of the servo bands SB1. And between each two of the servo readelements SH are provided a plurality of recording elements WH ranging intwo lines in the lateral direction of the magnetic tape MT in order torecord signals on the data bands DB1. Furthermore, between the recordingelements WH are provided a plurality of reproducing elements RH rangingin one line in the lateral direction of the magnetic tape MT.

When for the magnetic tape MT thus described, data isrecorded/reproduced with the magnetic head H of a magnetic tape drive(not shown), the servo signals SS1 are read with the servo read elementsSH. Since the servo patterns SP1 of the servo signals SS1 are slantedfor the travel direction (equal to a longitudinal direction) of themagnetic tape MT and are formed by respective unparallel stripes, atiming when the servo read elements SH read the servo signals SS1 anddetect a pulse differs in accordance with relative positions in thelateral direction of the magnetic tape MT and the magnetic head H.Therefore, the recording elements WH or the reproducing elements RH canbe accurately positioned onto predetermined tracks of the data bands DB1by controlling a position of the magnetic head H so that a timing forreading the pulse becomes a predetermined condition.

Then, an output (peak voltage value) with which the servo read elementsSH read the servo signals SS1 depends on a change rate or change amountof a change-over between a portion where no signal is recorded andanother portion where signals are recorded. And in the embodiment amagnetic direction largely varies from the forward direction to thereverse direction at a change portion from the base portion of the servobands SB1 magnetized in the forward direction to the servo patterns SP1magnetized in the reverse direction. In addition, the magnetic directionlargely varies from the reverse direction to the forward direction alsoat a change portion from the portion of the servo patterns SP1magnetized in the reverse direction to the base portion of the servobands SB1 magnetized in the forward direction. Therefore, depending onthe large magnetic change, as shown in FIG. 6B, the servo signals SS1can be read with a high output. Accordingly, the SN ratio of readsignals of the servo signals SS1 can be improved.

In addition, since in the magnetic tape MT magnetized by the servowriter 20A of the embodiment the data bands DB1 thereof are demagnetizedby the AC demagnetizing head 27, magnetic signals recorded in the databands DB1 are not influenced by other magnetizations. Accordingly, themagnetic signals can be surely recorded.

In addition, since the magnetic tape MT magnetized by the servo writer20A of the embodiment is narrower in a data track width thereof, thetape MT can be effectively used, particularly when it is used for amagnetic tape whose magnetic layer is thinner and a magnetic tape drivewhere a width of the servo read elements SH for reading the servo signalSS1 is narrower. That is, since conventionally a care must be taken fora saturation phenomenon of the MR element, it was avoided to write servosignals magnetized in the reverse direction on a portion magnetized by adirect current; however when making the magnetic layer thinner and thedata track width narrower in order to enlarge a memory capacity pervolume, the configuration of the present invention, which can get a readoutput of the servo signals with a high output, becomes suitable.

As such a magnetic tape is preferable a case that an Mrt (product of amagnetic layer residual magnetization Mr and a thickness t of a magneticlayer) is 5.0×10⁻¹⁰ T·m (4.0×10⁻² memu/cm²) to 7.5×10⁻⁸ T·m (6.0memu/cm²) is more preferable another case that 5.0×10⁻¹⁰ T·m (4.0×10⁻²memu/cm²) to 5.0×10⁻⁸ T·m (4.0 memu/cm²); and is most preferable stillanother case that 5.0×10⁻¹⁰ T·m (4.0×10⁻² memu/cm²) to 2.5×10⁻⁸ T·m (2.0memu/cm²).

In addition, a Tw (track width of a servo read element) is preferable ina case of 0.1 μm to 30 μm, more preferable in another case of 0.1 μm to15 μm, and most preferable in still another case of 0.1 μm to 7 μm.

Furthermore, the thickness of the magnetic layer is preferable in a caseof 10 nm to 300 nm, more preferable in another case of 10 nm to 200 nm,and most preferable in still another case of 10 nm to 100 nm.

Describing suitable examples of magnetic tapes of the present inventionin more detail, magnetic tapes, which have a non-magnetic layer and amagnetic layer on one face of a support body and a back layer on theopposite face thereof, are preferable. In addition, in a magneticrecording medium of the present invention the magnetic recording medium,which has layers other than the non-magnetic layer, the magnetic layer,and the back layer, are also included. For example, the recording mediummay has a soft magnetic layer containing soft magnetic powders, a secondmagnetic layer, a cushion layer, an overcoat layer, an adhesion layer,and a protection layer. These layers can be provided at adequatepositions so as to effectively bring out their functions. A thickness ofthe non magnetic layer can be made 0.5 μm to 3 μm: the thickness of thenon magnetic layer is desirable to be thicker than that of the magneticlayer.

Although a ferromagnetic powder for use in the magnetic layer of themagnetic recording medium of the present invention is not specificallyrestricted, a ferromagnetic metal powder and a hexagonal ferrite powderare preferable.

An average particle size of the ferromagnetic powder is preferably 20 nmto 60 nm. When the ferromagnetic powder for use in the present inventionis acicular and the like, the average particle size represented by anaverage long axis length is preferably 30 nm to 45 nm, and an averageacicular ratio is preferably 3 to 7; when the ferromagnetic powder isplaty, the average particle size is represented by an average platediameter, it is preferably 25 nm to 35 nm, and an average plate ratio ispreferably 2 to 5.

In the ferromagnetic metal powder, an S_(BET) (specific surface area ofthe BET (Brunauer, Emmett and Teller) method) is usually 40 m²/g to 80m²/g and preferably 50 m²/g to 70 m²/g. A crystal size is usually 10 nmto 25 nm and preferably 11 nm to 22 nm. A pH of the ferromagnetic metalpowder is preferably not less than 7. As the ferromagnetic metalpowders, a single material and alloy of Fe, Ni, Fe—Co, Fe—Ni, Co—Ni,Co—Ni—Fe, and the like are cited, and within a range of not more than 20mass percent of metal compositions can be contained aluminum, silicon,sulfur, scandium, titan, vanadium, chromium, manganese, copper, zinc,yttrium, molybdenum, rhodium, palladium, gold, tin, antimony, boron,barium, tantalum, tungsten, renium, silver, lead, phosphorus, lanthanum,cerium, praseodymium, neodymium, tellurium, bismuth, and the like. Inaddition, the ferromagnetic metal powders may also contain a smallamount of water, a hydroxide, and an oxide. Manufacturing methods ofthese ferromagnetic metal powders are already well known andferromagnetic metal powders for use in the present invention can also bemanufactured in accordance with well known methods. Although shapes ofthe ferromagnetic metal powders are not particularly restricted, usuallyan acicular shape, a grit shape, a cubic shape, a rice grain shape, aplate shape, and the like are used. It is specifically preferable to useacicular ferromagnetic metal powders.

A resistance magnetism Hc of the ferromagnetic metal powders ispreferably 144 kA/m to 300 kA/m and more preferably 160 kA/m to 224kA/m. In addition, a saturation magnetization thereof is preferably 85A·m²/kg to 150 A·m²/kg and more preferably 100 A·m²/kg to 130 A·m²/kg.

As the hexagonal ferrite powders there are a barium ferrite, a strontiumferrite, a lead ferrite, a calcium ferrite, and various replacementmaterials, for example, a Co replacement material, and the like. To bemore precise, are cited a magnetoplumbite type of barium ferrite andstrontium ferrite, the magnetoplumbite type of ferrite whose particlesurface is covered with spinel, further a compound magnetoplumbite typeof barium ferrite and strontium ferrite that partially contain a spinelphase, and the like; and other than predetermined elements, followingones may be contained: Al, Si, S, Ba, Nb, Sn, Ti, V, Cr, Cu, Y, Mo, Rh,Pd, Ag, Sb, Te, W, Re, Au, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, B, Ge,and the like. Generally, the hexagonal ferrite powder where followingcompounds are added can be used: Co—Zn, Co—Ti, Co—Ti—Zr, Co—Ti—Zn,Ni—Ti—Zn, Nb—Zn—Co, Sn—Zn—Co, Sn—Co—Ti, Nb—Zn, and the like. Somehexagonal ferrite powders contain a specific impurity in accordance withmaterials and/or manufacturing methods. The hexagonal ferrite powdersare a hexagonal plate shape.

When reproducing with a magnetic resistant head (MR head) toparticularly raise a track density, it is requested to make a noise low:if an average plate diameter is too small, a stable magnetization cannotbe desired due to heat fluctuations. In addition, if the average platediameter is too large, the noise is high, thereby both cases being unfitfor the high density recording. Although if the average plate ratio issmall, a filling property in the magnetic layer becomes large and it ispreferable, a sufficient orientation cannot be obtained. If the fillingproperty is too large, the noise becomes high due to stacking betweenpowders. The specific surface area in accordance with the BET method isusually 30 m²/g to 200 m²/g, and 50 m²/g to 100 m²/g is preferable. Thespecific surface area generally accords with an arithmetic calculationvalue from a powder plate diameter and a thickness thereof. Adistribution of the plate diameter and the thickness is preferable to benarrower. Although many distributions are not a normal distribution withbeing calculated in a standard deviation for a powder size, it isexpressed as σ/(average plate diameter or average thickness)=0.1 to 0.5.In order to make a powder size distribution sharp, it is performed tomake a powder generation-reaction system uniform as much as possible andto also dispense a distribution improvement treatment to a generationpowder. For example, such a method of selectively dissolving an ultraminuscule powder in an acid solution is also known. In avitrification-crystallization method a more uniform powder is obtainedby performing heat treatments plural times and separating nucleusgeneration and growth. Although the resistance magnetism Hc measured ina magnetic powder can be made till around 40 kA to 400 kA, 144 kA to 300kA is preferable. Although a high Hc is advantageous in the high densityrecording, an ability of a recording head is restricted. An Hc can becontrolled by the powder size (plate diameter and plate thickness),kinds and amounts of contained elements, replacement sites of elements,powder generation-reaction conditions, and the like.

A saturation magnetization σs is preferably 30 A·m²/kg to 70 A·m²/kg.The σs tends to become smaller as a powder becomes minuscule. Formanufacturing methods thereof, there are a method of lesseningcrystallization temperature or heat treatment time, another method ofincreasing addition compounds, still another method of increasing anamount of surface treatment, and the like.

In addition, it is possible to use a W type of a hexagonal ferrite. Indispersing the magnetic material a surface of a magnetic powder is alsotreated with a dispersion medium and a material matching a polymer. Aninorganic compound and an organic compound are used as a surfacetreatment agent. As main compounds typical examples are: an oxide andhydroxide of Si, Al, P, and the like; various silane coupling agents;and various titan coupling agents. An amount thereof is 0.1 to 10 masspercent for a magnetic material. A pH thereof is also important fordispersion. It is usually around 4 to 12, and although there is anoptimum value in accordance with the dispersion medium and the polymer,around 6 to 11 is selected from a chemical stability and storagestability of the magnetic recording medium. A water content contained inthe magnetic material also influences the dispersion. Although there isan optimum value thereof in accordance with the dispersion medium andthe polymer, usually 0.1 to 2.0 mass percent is selected. The presentinvention does not select manufacturing methods although there aremethods as follows: (1) a vitrification-crystallization method of mixingmetal oxides, which replaces a barium carbonate, an iron oxide, and aniron, with such a boron oxide as a glass forming material so as tobecome a predesired ferrite composition, then melting it, making anamorphous material by rapid cooling, next dispensing a reheatingtreatment, and then cleaning and pulverizing it, thereby obtaining abarium ferrite crystalline powder; (2) a water-heat reaction method ofneutralizing a metal salt solution of a barium ferrite composition withalkali, removing byproducts, then heating it in a liquid phase at notless than 100 degrees Celsius, and then cleaning and pulverizing it,thereby obtaining the barium ferrite crystalline powder; and (3) acoprecipitation method of neutralizing the metal salt solution of thebarium ferrite composition with alkali, removing byproducts, then dryingit, performing a heat treatment at not more than 1100 degrees Celsius,and pulverizing it, thereby obtaining the barium ferrite crystallinepowder.

[Second Embodiment]

The second embodiment of a servo writer related to the present inventionwill be described, referring to FIG. 7 as needed. FIG. 7 is aconfiguration drawing of a servo writer of the second embodiment.Meanwhile, in the embodiment same symbols will be appended to sameportions as in the first embodiment and descriptions thereof will beomitted.

The servo writer 20B of the embodiment is a servo writer for recording aservo signal on the magnetic tape MT demagnetized all over a surfacethereof in advance: in the manufacturing process shown in FIG. 5 theservo writer 20B is for writing the servo signal on the magnetic tape MTdemagnetized in a demagnetizing process (not shown) that is furtherprovided after the drying process 13 thereof.

As shown in FIG. 7, the servo writer 20B mainly comprises a supply reel21 b, the winder 22, the drive unit 23, a pulse generation circuit 24 b,the servo write head 25, a DC demagnetizing head 28, a control unit 26b, the first guides 29 a, and the second guides 29 b. Meanwhile, thewinder 22, the drive unit 23, the first guides 29 a, and the secondguides 29 b are same ones used in the servo writer 20A of the firstembodiment.

The supply reel 21 b is configured same as the supply reel 21 a (seeFIG. 1) used in the first embodiment except that the magnetic tape MTdemagnetized all over the surface thereof in advance is wound around thesupply reel 21 b.

The pulse generation circuit 24 b is configured same as in the pulsegeneration circuit 24 a used in the first embodiment, so as to generatethe recording current pulses PC1 (see FIG. 6C) for writing the servosignal in the servo write head 25, and is configured so as tocontinuously give a direct current demagnetizing current to the DCdemagnetizing head 28.

The control unit 26 b generates, same as the control unit 26 a used inthe first embodiment, the motor current signal for controlling the motorcurrent of the drive unit 23, and is configured so as to generate thepulse control signal for generating the recording current pulses PC1 atthe pulse generation circuit 24 b. Moreover, the control unit 26 bgenerates a demagnetization control signal for generating the directcurrent demagnetization current at the pulse generation circuit 24 b,and is configured so as to send the demagnetization control signal tothe circuit 24 b.

The servo write head 25 and the DC demagnetizing head 28 are integrallyconfigured with each base thereof being connected to a support member 30b fixed at a platform not shown, and both tops of the servo write head25 and the DC demagnetizing head 28, which extend from the supportmember 30 b and respectively slide in contact with the magnetic tape MT,form a gap with a distance. In the gap a pair of the first guides 29 aconfigured same as in the first embodiment are designed to be arranged.However, the first guides 29 a used in the embodiment are different fromthose of the first embodiment (see FIG. 1) in nothing except for a pointthat the former are connected through the disc springs 31 to a shaftmember (not shown) for supporting the second guides 29 b that arearranged at an upstream side of a magnetic tape travel direction of theDC demagnetizing head 28.

The DC demagnetizing head 28 is a head for magnetizing a portioncorresponding to servo bands of the magnetic tape MT by a directcurrent, and comprises a coil (not shown) generating a magnetic flux bythe direct current magnetization current being given from the pulsegeneration circuit 24 b. And magnetic gaps (not shown) for a directcurrent demagnetization are provided at corresponding positions of theservo bands the magnetic tape MT on a sliding contact surface of thetape MT of the DC demagnetizing head 28.

Next, operation of the servo writer 20B of the embodiment will bedescribed, referring to FIG. 8. FIG. 8 is an enlarged plan viewillustrating a magnetization condition of a magnetic tape magnetized bya servo writer related to the embodiment.

On the supply reel 21 b of the servo writer 20B (see FIG. 7) is set thepancake shape of the magnetic tape MT demagnetized all over the surfacethereof in advance. Then, the DC demagnetizing head 28 magnetizes theportion, corresponding to the servo bands of the magnetic tape MT by thedirect current, which tape MT is sent out of the supply reel 21 b andruns by being wound by the winder 22. And as shown in FIG. 8, same as inthe first embodiment, the servo write head 25 forms the servo patternsSP1 magnetized in the reverse direction on the base portion of the servobands SB1 magnetized in the forward portion. Of course, a portion of theservo bands SB1 except for the servo patterns SP1 is magnetized in theforward direction as it is.

In such the servo writer 20B of the embodiment the servo write head 25and the DC demagnetizing head 28 are integrally configured, and thefirst guides 29 a regulate a movement in the lateral directions of themagnetic tape MT running between the servo write head 25 and the DCdemagnetizing head 28 by an energizing force of the disc springs 31(seeFIG. 7). As a result, in the servo writer 20B a sliding contact surfaceof the DC demagnetizing head 28 with the magnetic tape MT is generallylong, so even if a distance between the second guides 29 b (see FIG. 7)arranged at the upstream/downstream sides of the DC demagnetizing head28 is obliged to be taken wide, the magnetic tape MT is not oscillatedin the lateral directions thereof between the servo write head 25 andthe DC demagnetizing head 28. Accordingly, the servo writer 20B of theembodiment can accurately leave a magnetization in the forward directionof the portion of the servo bands SB1. In addition, since in accordancewith the servo writer 20B of the embodiment a curvature of the servobands SB1 extending in the longitudinal directions of the magnetic tapeMT can be restrained by preventing the oscillation of the lateraldirections of the magnetic tape MT, the position error signal (PES) isreduced.

The magnetic tape MT where a magnetization treatment is performed bysuch the servo writer 20B has a plurality of the servo bands SB1extending in the longitudinal directions of the magnetic tape MT and oneof the data bands DB1 positioned between each two of the servo bandsSB1. Each of the servo bands SB1 is magnetized in the magnetic tapetravel direction (forward direction) of the longitudinal directions. Andthe servo signals SS1 are written with magnetizing each of the servobands SB1 in the reverse direction. Meanwhile, a magnetization treatmentis not performed for each of the data bands DB1 between each two of theservo bands SB1 by the servo writer 20B. Thus, the magnetic tape MT,where the servo signals SS1 are written and which is wound on the winder22, is slit into a tape length, depending on a product specification,and is housed in a cartridge case and the like (not shown).

For the magnetic tape MT thus described, in recording/reproducing datasame as in the first embodiment by the magnetic head H (see FIG. 6) of amagnetic tape drive (not shown), an output (peak voltage value) withwhich the servo read elements SH read the servo signals SS1 depends on achange rate or change amount between a portion where no signal isrecorded and another portion where signals are recorded. And in theembodiment a magnetic direction largely varies from the forwarddirection to the reverse direction at a change portion from the baseportion of the servo bands SB1 magnetized in the forward direction tothe servo patterns SP1 magnetized in the reverse direction. As a result,same as in the first embodiment, since the servo signals SS1 can be readwith a high output, the SN ratio of read signals of the servo signalsSS1 can be improved.

Thus, although the first and second embodiments of the present inventionare described, the invention is not limited thereto and is implementedin various forms without departing from the spirit and scope of theinvention.

For example, although in the first embodiment the first guides 29 a areattached through the disc springs 31 to the shaft member 33 forsupporting the second guides 29 b, the servo writers of the presentinvention are not limited thereto, and they may use a servo write headassembly where the servo write head 25 and the AC demagnetizing head 27are integrally configured.

As shown in FIGS. 9A and 9B, a servo write head assembly 40 comprises asupport member 30 c and a pair of disc springs 31 a; wherein the supportmember 30 c connects the servo write head 25 and the AC demagnetizinghead 27 so as to be integrally configured; and wherein bases of the discsprings 31 a are connected to the support member 30 c, the first guides29 a are rotatably supported by tops of the disc springs 31 a extendingfrom the support member 30 c, and thus the first guides 29 a arearranged between the servo write head 25 and the AC demagnetizing head27 by the pair of the disc springs 31 a. Meanwhile, FIG. 9B is a sectionview taken along a line Y—Y of FIG. 9A that is a perspective view of theservo write head assembly 40.

In accordance with the servo write head assembly 40, same as in theservo writer 20A of the first embodiment the servo write head 25 and theAC demagnetizing head 27 are integrally configured, and the first guides29 a regulate a movement in the lateral directions of the magnetic tapeMT running between the servo write head 25 and the AC demagnetizing head27 by the energizing force F of the disc springs 31 a. As a result, in aservo writer comprising the servo write head assembly 40 a slidingcontact surface of the AC demagnetizing head 27 with the magnetic tapeMT is generally long, so even if a distance between the second guides 29b (see FIG. 1) arranged at the upstream/downstream sides of the ACdemagnetizing head 27 is obliged to be taken wide, the magnetic tape MTis not oscillated in the lateral directions thereof between the servowrite head 25 and the AC demagnetizing head 27. Accordingly, same as inthe first embodiment, the servo writer comprising the servo write headassembly 40 can accurately demagnetize nothing except for the portion ofthe data bands DB1 and leave a magnetization in the forward direction ofthe portion of the servo bands SB1. In addition, since in accordancewith the servo write head assembly 40 the curvature of the servo bandsSB1 extending in the longitudinal directions of the magnetic tape MT canbe restrained by preventing the oscillation of the lateral directions ofthe magnetic tape MT, the position error signal (PES) is reduced.

In addition, although in the servo write head assembly 40 the firstguides 29 a are attached through the disc springs 31 a to the supportmember 30 c for connecting the servo write head 25 and the ACdemagnetizing head 27 so as to be integrally configured, an attachmentstructure of the first guides 29 a in the servo write head assembly 40may be applied to the servo writer 20B of the second embodiment. Thatis, the servo writers of the present invention may also be ones thatcomprise a servo write head assembly where the first guides 29 a areattached through disc springs to a support member (not shown) forconnecting the servo write head 25 and the AC demagnetizing head 27 soas to be integrally configured.

In addition, although in the first and second embodiments a recordingcurrent is designed to consist of a pulse current where a pulse currentof a plus polarity and a zero current are alternately repeated, notlimited to this pattern, another pulse current where a pulse current ofa minus polarity and a zero current alternately repeated may also beused.

In addition, although in the first and second embodiments a base portionof servo bands is magnetized in the forward direction and a portion ofservo signals is magnetized in the reverse direction, on the contrarythe base portion of the servo bands may be magnetized in the reversedirection and the portion of the servo signals may be magnetized in theforward direction.

In addition, although in the first embodiment the AC demagnetizing head27 is arranged at the downstream side of the magnetic tape traveldirection of the servo write head 25, in the servo writers of thepresent invention the AC demagnetizing head 27 may be arranged at theupstream side of the magnetic tape travel direction of the servo writehead 25.

In addition, although in the first and second embodiments the discsprings 31 are attached to a shaft member for supporting one of thesecond guides 29 b that are arranged at the upstream and downstream sideof the first guides 29 a, the shaft member where the disc springs 31 areattached may be any one of shaft members of the second guides 29 barranged at-the upstream and downstream sides of the first guides 29 a.

Although the first guides 29 a exemplified in the first and secondembodiments (see FIG. 3) and the first guides 29 a used for the servowrite head assembly 40 (see FIG. 9) are configured of the rollerportions 32 a for holding down the surface of the magnetic tape MT withcircumferential surfaces thereof and the flanges 32 b, which are formedat the roller portions 32 a, for holding down the side edges of themagnetic tape MT that is running, and the first guides 29 a arerotatably supported by the disc springs 31 or 31 a (see FIGS. 2 and 9),the present invention is not limited thereto. That is, first guides usedfor servo writers of the present invention may not always comprise theroller portions 32 a, and for example, may also be a disc shape of thefirst guides that press both side edges of the magnetic tape MT with onesurface thereof.

1. A servo write head assembly comprising: an AC demagnetizing head thatslides in contact with a magnetic tape all of which surface ismagnetized in one direction of longitudinal directions thereof, anddemagnetizes a data band of the magnetic tape; a servo write head thatslides in contact with said magnetic tape, magnetizes a servo band ofthe magnetic tape in a reverse direction, and writes a servo signal; anda guide for regulating a movement in lateral directions of said magnetictape that is running, wherein said AC demagnetizing head and said servowrite head are integrally configured, and said guide is provided betweensaid AC demagnetizing head and said servo write head, and wherein saidservo band comprises a plurality of servo signals which provide controlinformation for reading data from or recording data onto said data band.2. A servo write head assembly according to claim 1, wherein said guideis comprised of a roller portion and a flange formed in said rollerportion, wherein said roller portion holds down a surface of saidmagnetic tape with circumferential surfaces thereof, and wherein saidflange holds down side edges of said magnetic tape that is running.
 3. Aservo write head assembly according to claim 2, wherein said guidecomprises a first guide disposed on one side in lateral directions ofthe magnetic tape and a second guide disposed on the other side inlateral directions of the magnetic tape, and the magnetic tape is heldfrom both lateral sides by first and second guides.
 4. A servo writehead assembly according to claim 1 which comprises a disc spring forpushing said guide in lateral directions of said magnetic tape, whereinone end of the disc spring is attached to said guide, and the other endof said disc spring is attached to a support member for connecting saidAC demagnetizing head and said servo write head so as to be integrallyconfigured.
 5. A servo write head assembly according to claim 1, whereinsaid guide pushes both side edges of said magnetic tape oscillating inlateral directions with an energizing force of 0.490×10⁻² to 7.84×10⁻²N.
 6. The servo write head assembly according to claim 1, furthercomprising a support member for connecting said AC demagnetizing headand said servo write head so as to be integrally configured.
 7. A servowrite head assembly according to claim 1, wherein said guide comprises afirst guide disposed on one side in lateral directions of the magnetictape and a second guide disposed on the other side in lateral directionsof the magnetic tape, and the magnetic tape is held from both lateralsides by first and second guides.
 8. A servo write head assemblyaccording to claim 1, wherein the servo band and the data band arealternately positioned in the longitudinal directions of the magnetictape.
 9. A servo writer comprising: a magnetic tape running system thatsends a magnetic tape, all of which surface is magnetized in onedirection of longitudinal directions, out of a supply reel, and windssaid magnetic tape with a winder, thereby running the magnetic tape; anAC demagnetizing head that slides in contact with said magnetic tapethat is running, and demagnetizes a data band of the magnetic tape; aservo write head that slides in contact with said magnetic tape,magnetizes a servo band of the magnetic tape in a reverse direction, andwrites a servo signal; and a guide for regulating a movement in lateraldirections of said magnetic tape that is running, wherein said ACdemagnetizing head and said servo write head are integrally configured,and said guide is provided between said AC is demagnetizing head andsaid servo write head, wherein said servo band comprises a plurality ofservo signals which provide control information for reading data from orrecording data onto said data band.
 10. A servo writer according toclaim 9, wherein said guide is comprised of a roller portion and aflange formed in said roller portion, wherein said roller holds down asurface of said magnetic tape with circumferential surfaces thereof, andwherein said flange holds down side edges of said magnetic tape that isrunning.
 11. A servo writer according to claim 9 which comprises a discspring for pushing said guide in lateral directions of said magnetictape, wherein one end of the disc spring is attached to said guide, andthe other end of said disc spring is attached to a shaft member providedat an upstream side of a magnetic tape travel direction of said ACdemagnetizing head and said servo write head.
 12. A servo writeraccording to claim 9 which comprises a disc spring for pushing saidguide in lateral directions of said magnetic tape, wherein one end ofthe disc spring is attached to said guide, and the other end of saiddisc spring is attached to a shaft member provided at a downstream sideof a magnetic tape travel direction of said AC demagnetizing head andsaid servo write head.
 13. A servo writer according to claim 9, whereinsaid guide pushes both side edges of said magnetic tape oscillating inlateral directions with an energizing force of 0.490×10⁻² to 7.84×10⁻²N.
 14. A servo writer according to claim 9, wherein said guide pushesboth side edges of said magnetic tape oscillating in lateral directionswith an energizing force of 0.490×10⁻² to 3.92×10⁻² N.
 15. The servowriter according to claim 9, further comprising a support member forconnecting said AC demagnetizing head and said servo write head so as tobe integrally configured.
 16. A servo writer according to claim 9,wherein the servo band and the data band are alternately positioned inthe longitudinal directions of the magnetic tape.
 17. An ACdemagnetizing head assembly comprising: a guide for regulating amovement in lateral directions of a magnetic tape all of which surfaceis magnetized in one direction of longitudinal directions thereof; adisc spring for pushing said guide in lateral directions of saidmagnetic tape, wherein the disc spring is attached to one end of theguide; and a support member attached to the other end of the discspring, wherein the AC demagnetizing head assembly slides in contactwith the magnetic tape, demagnetizes a data band of the magnetic tape,magnetizes a servo band of the magnetic tape in a reverse direction ofsaid one direction, and writes a servo signal onto said servo band.